Electronically tunable parametric amplifier of extended tuning range with pump wave loading means



May 16, 1 HSIUNG VHSU ETAL 3,320,542 EXTENDED ELECTRONICALLY TUNABLEPARAMEJTRIC AMPLIFIER OF TUNING RANGE WITH PUMP WAVE LOADING MEANSOriginal Filed Sept. 29, 1961 3 Sheets-Sheet 1 Gmmzw 255 o wugowINVENTORSZ HSIUNG HSU STEPHEN WANUGA,

THEIR ATTORNEY.

y 1967 HSIUNG HsU ETAL 3,320,542

XTENDED ELECTRONICALLY TUNABLE PARAMETRIC AMPLIFIER OF E TUNING RANGEWITH PUMP WAVE LOADING MEANS 3 Sheets-Sheet 2 Original Filed Sept. 29,1961 l' 5' n o W- nu in Q ot'ufl-no' INVENTORSI HSIUNG Hsu, STEPHENWANUGA,

BY W

THEIR ATTORNEY.

3,320,542 XTENDED May 16, 19 7' HSIUNG HSU ETA-L ELECTRONICALLY TUNABLEPARAMETRIC AMPLLFIER OF E TUNING RANGE WITH PUMP WAVE LOADING MEANSOriginal Filed Sept. 29, 1961 3 Sheets-Sheet 3 SOURCE OF SIGNAL ENERGYSOURCE OF PUMP ENERGY "I l 93 I Li 93W FIG.9.

INVENTORS I A u w N m G NN i S P E T 5 THEIR ATTORNEY" United StatesPatent 3,320,542 ELECTRQNICALLY TUNABLE PARAMETRIC AM- PLllFlER 0FEXTENDED TUNING RANGE WITH PUMP WAVE LOADING MEANS Hsiung Hsu, Columbus,Ohio, and Stephen Wanuga, Liverpool, N.Y., assignors to General ElectricCompany, a corporation of New York (Yontinuation of application Ser. No.141,873, Sept. 29, 1961. This application June 12, 1964, Ser. No.376,294 6 Claims. (Cl. 3304.6)

The present invention relates to novel tunable parametric amplifiers ofextended tuning range, and in particular to traveling wave typeparametric amplifiers having a narrow band width and which areelectronically tunable over an extended frequency range. The presentinvention constitutes an improvement of an electronically tunabletraveling wave parametric amplifier of the type disclosed in ourcopending application for US. Letters Patent entitled, ElectronicallyTunable Parametric Amplifier, Ser. No. 88,535, filer Feb. 10, 1961, nowPatent No. 3,193,772.

The present patent application is a continuation of applicants copendingapplication for US. Letters Patent, Ser. No. 141,873, file-d Sept. 29,1961, now abandoned, and assigned to the assignee of the presentinvention.

Parametric amplifiers are well known in the prior art to provideamplification of a high frequency signal of frequency w, by convertingpower to said signal from a second wave of a higher frequency, termedthe pump frequency to The signal frequency m and the pump frequency oare mixed in a nonlinear device. A resonant circuit is provided withsaid nonlinear device which resonates at the difference frequency of thetwo applied Waves, conventionally termed the idler frequency m The idlerfrequency is applied to the nonlinear device and mixed with the pumpfrequency to again obtain the signal frequency. Since the pump frequencyis greater than the idler and signal waves, the flow of power in thesystem is from the pump to the idler to the signal wave, in accordancewith known Manley-Rowe relations. The flow of power at the idlerfrequency introduces a negative resistance into the signal circuit sothat the signal wave is taken at the output of the nonlinear device asan amplified signal. In the simple standing wave type amplifier,parametric amplification will occur so long as the relationship w =w +wis satisfied.

Recently electronically tunable parametric amplifiers have beendeveloped which employ traveling waves, as opposed to standing waves incavity type amplifiers. By electronically tunable it is meant that theamplifier is tuned by varying the pump frequency with an electricalsignal. By way of definition, traveling wave parametric amplifiers maybe classified into essentially two categories: (a) the forward or simplytraveling wave type parametric amplifier wherein the signal phasevelocity V, and the signal group velocity V are along the forwarddirection with respect to the pump wave, or are both of positive value,and (b) the backward traveling wave type parametric amplifier wherein V,and V are along the backward direction with respect to the pump wave, orare both of negative value. In addition, there are what may beconsidered backward wave parametric amplifiers wherein V,, and V are ofopposite sign.

Traveling wave parametric amplifiers are conventionally constructed of atransmission medium comprising, for example, a wave guide, strip line,coaxial cable, or combination thereof, which are periodically loadedwith nonlinear reactance active elements, such as capacitors, reactancediodes, inductors or ferrite slabs. Whereas in a cavity type parametricamplifier interaction of the mixed frequencies occurs at the same one ortwo active elements 3,320,542 Patented May 16, 1967 disposed in astanding wave pattern during many cycles of operation, in the travelingwave type amplifier the interaction occurs at a large number of activeelements, and usually each element is perturbed only once by each waveof the traveling waves as they are propagated through the transmissionmedium. Since traveling transmission media are able to supportcontinuous bands of frequencies, electronic tuning of the amplifier overa wide band of frequencies can be accomplished. A further description oftunable parametric amplifiers may be found in an article by P. K. Tienentitled, Parametric Amplification and Frequency Mixing in PropagatingCircuits, appearing in the Journal of Applied Physics, vol. 29, No. 9,September, 1958, and a low frequency embodiment is described in anarticle by D. I. Brietzer and E. W. Sard entitled, Low FrequencyPrototype Backward Wave Reactance Amplifier, appearing in the MicrowaveJournal, vol 2, No. 8, August 1959.

In the prior art, as for example described in the aforementionedpublications, it has been possible to tune the amplifier by maintainingthe ratio of w /w constant. Although this frequency constraint permitsselective tuning, for high frequency signals in the order of hundreds ofmegacycles, the pump frequency, which is required to be considerablyhigher than the signal for good amplification, must be tuned over anexceedingly widerange for signal frequency variations. For example, ifthe signal frequency is varied from 250-500 megacycles, the pumpfrequency is required to vary by the same ratio from, let us say,2000-4000 megacycles. Since there is an inherent limitation in the rangeof adjustment of such high frequency pump sources, the band throughwhich the signal frequency can vary, and hence the amplifier tuningrange, is accordingly limited.

The above referred to copending application Ser. No. 88,535 relates totraveling wavetype parametric amplifiers of various configurations inwhich the signal wave can be tuned over an enhanced tuning range. Thereis presented in said copending application the frequency and phaseconstant restraints required for effective parametric amplification oftraveling waves, namely where {3 denotes the phase constant of thetravelingwaves. The tuning range is enhanced by maintaining operation ofthe idler wave at approximately constant frequency and varying the phaseconstant such that the above required constraints are always satisfield.In this manner, the pump frequency is required to vary by approximatelythe same amount as the signal frequency rather than by the sameproportion as before. Thus, if the signal frequency is varied from 250to 500 megacycles, the pump frequency need only change from 2000megacycles to 2250 megacycles.

The present invention further improves the tuning capabilities of atraveling wave parametric amplifier providing a further enhancement ofthe signal frequency tuning range and permitting tuning of the signalwave at a higher frequency than previously realizable.

It is accordingly an object of the present invention to provide animproved electronically tunable parametric amplifier which may beemployed to selectively amplify high frequency signals tunable over anenhanced frequency band.

A further object of the present invention is to provide a novelelectronically tunable traveling wave parametric amplifier which canpropagate a Wide range of pump fre quencies so as to permit signaltuning over an enhanced frequency band.

Another object of the present invention is to provide an improvedelectronically tunable parametric amplifier of the type above describedhaving a reduced noise characteristic.

These and other objects of the invention are accomplished in oneembodiment thereof which is in the form of a backward traveling waveparametric amplifier. The amplifier may be of the type which includes awave guide structure in which is propagated a pump wave. Signal andidler waves may be propagated along a center conductor enclosed by theguide and running parallel to the longitudinal dimension thereof, thedirection of the propagation of the signal wave being opposite to thatof the pump. The amplifier is successively loaded by nonlinear reactancediodes which are coupled between the center conductor and the widedimension walls of the wave guide at spaced intervals along thelongitudinal dimension of the guide. The idler wave is produced by theinteraction of the pump and signal waves across the reactance diodes. Inorder for parametric amplification to occur, the three waves must berelated so that the following constraints are satisfied: (1) the pumpfrequency is equal to the signal frequency plus the idler frequency; and(2) the pump phase constant is equal to the signal phase constant plusthe idler phase constant. The waves propagated by the wave guide andcenter conductor exhibit frequency versus phase constant functions whichare determined by the properties of their respective transmission paths.The idler wave is preferably operated on the dispersive portion of thefrequency versus phase constant function of the idler wave so that thesignal can be tuned over a wide range while satisfying the aboveconstraints. In addition to the nonlinear loading necessary forparametric amplification, in accordance with the present invention thepump wave alone is further successively loaded which expands thefrequency versus phase constant function of the pump wave so thatgreater linear portion of the function and hence higher pump frequenciesare available for the tuning operation. This has the desirable effect ofboth increasing the range over which the signal may be tuned andallowing for the tuning of a higher signal frequency. The additionalloading of the pump wave is provided by a succession of loading stubswhich are coupled between the wide dimension walls of the wave guide atpoints intermediate the reactance diodes, said loading stubs beingpositioned to have negligible loading effect on the center conductor.

- In accordance with another aspect of the invention, there is provideda traveling wave parametric amplifier in which the pump wave ispropagated through a wave guide structure, and the signal and idlerwaves are propagated along a longitudinal conductor which is enclosed ina compartment adjoining said wave guide structure. The conductor iselectrically coupled to the energy propagated within said wave guide bysuccessively spaced transverse conductors, said reactance elementssuccessivecoupled between the longitudinal conductor and said transverseconductors, said reactance elements succesively loading the pump, signaland idler waves at spaced intervals along the longitudinal dimension ofthe wave guide, thereby effecting parametric amplification. In addition,loading stubs are coupled between the wide dimension walls of the waveguide at points intermediate the reactance diodes which stubs areessentially uncoupled from said transverse conductors so as to load onlythe pump wave.

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter which is regarded as theinvention, it is believed that the invention will be better understoodfrom the following description taken in connection with the accompanyingdrawings in which:

FIGURE 1 illustrates a perspective view of one embodiment of a backwardtraveling wave amplifier in accordance with the invention;

FIGURE 2 shows a cross-sectional view of the device of FIGURE 1 takenalong the plane 2-2',

FIGURE 3 shows a cross-sectional view of the device of FIGURE 1 takenalong the plane 3-3;

FIGURE 4 shows a cross-sectional view of the device of FIGURE 1 takenalong the plane 4-4;

FIGURE 5 illustrates an equivalent circuit of the parametic amplifier ofFIGURES 1-4;

FIGURE 6 illustrates Brillouin diagrams for the three traveling waves inthe amplifier of FIGURES 1-4 in which frequency a: is plotted versusphase constant B;

FIGURE 7 illustrates a perspective view of another embodiment of atraveling wave parametric amplifier in accordance with the invention;

FIGURE 8 illustrates a plan view, partially broken away, of the deviceof FIGURE 7;

FIGURE 9 illustrates a cross-sectional view of the device of FIGURE 7taken along the plane 9-9; and

FIGURE 10 illustrates a cross-sectional view of the device of FIGURE 7taken along the plane 10-10.

Referring now to FIGURE 1, there is illustrated a perspective view of anelectronically tunable parametric amplifier device 1, operated as abackward traveling wave amplifier. The device has applied thereto asignal to be amplified and a pump wave which provides power to thesignal. A source of signal energy 2, for example an antenna, applies thesignal wave to a connector 3 of device 1, and a source of pump energy 4,which may be a voltage tunable magnetron, applies the pump wave to aconnector 5. The amplifier signal appears at an output connector 6 andis applied to load 7. The pump wave output is coupled from connector 8to a pump load 9.

The amplifier device 1 includes a wave guide structure 10 which enclosesa single conductor 11 positioned in the center of the guide 10 andrunning along the longitudinal dimension thereof, as shown in thecrosssectional view of FIGURES 2 and 3. The wave guide structure 10supports propagation of the pump wave, and the center conductor 11supports propagation of both signal and idler waves. The centerconductor 11 is provided with periodic undulations, sinusoidal in formas illustrated in FIGURE 3, which increases the path length and thusdecreases the velocity of the signal and idler waves in the longitudinaldirection. Since the phase velocity is a function of the transmissionmedium, the phase velocities of the three waves can be predetermined.The phase velocities of the signal and idler waves as a function offrequency are equal in magnitude but opposite in direction. For tuningpurposes the phase velocity of the pump wave is made greater than thevelocity of the idler and signal waves. The relationship of thevelocities of the three waves is important in the tuning of theamplifier and will be subsequently analyzed in detail when consideringthe Brillouin diagrams of FIGURES 6 and the tuning requirements.

The amplifier device 1 is periodically loaded by a plurality of pairs ofreactance diodes 12-13, 14-15, 16-17, 18-19, 20-21 and 22-23 shown inFIGURE 2 which are coupled to the pump, signal and idler waves andacross which the three waves are mixed to provide parametricamplification. The diodes are electrically coupled between the widedimension walls 24 and 25 of the wave guide 10 and center conductor 11.The diodes are shown adjustably mounted by a plurality of threadedsleeves 26 which may be welded to the exterior of the Walls 24 and 25.The diodes, of matched impedance characteristics for maximum signalamplification, are uniformly spaced and coupled to center points ofconductor 11. In accordance with well known principles, the diodes arenormally self-biased for operation in the backward direction.

In addition, there are provided pairs of capacitive loading stubs 27-28,29-30, 31-32, 33-34 and 35-36 which are electrically coupled between thewide dimension walls 24 and 25, and positioned in such a manner as toperiodiin the upper frequency region is a function cally load the pumpenergy essentially without disturbing the field of the signal and idlerenergy.

As illustrated in the cross-sectional view of FIGURE 4, the centerconductor is located in a plane midway between walls 24 and 25, in whichplane the electric fields E and E between the conductor 11 and the walls24 and 25, respectively, are balanced, so that the energy propagated bythe conductor is isolated from the energy in the wave guide. Thispermits the pump, signal and idler energy upon traveling through thedevice 1 to react across the reactance diode loads in the prescribedmanner so that power is transferred from the pump to the signal whileensuring that the pump and signal energy is uncoupled at the input andoutput terminals. The loading stubs, as shown by stubs 29-30, increasethe electric field E between the walls 24 and 25 so as to additionallyload only the pump energy. The stubs are physically displaced in thetransverse direction from the center conductor 11 so that fields E and Bare negligibly affected by the loading stubs, and hence there isessentially no loading by the stubs of either the idler or signal waves.Thus, the pump wave is provided with loading at a periodic rate higherthan that of the signal and idler waves. This allows improved tuning ofthe signal over a range in which the w-fi plot of the pump wave issubstantially linear, as will be more clearly understood whenconsidering the equivalent circuit of FIGURE 5 and the Brillouindiagrams of FIGURE 6.

Referring now to FIGURE 5, there is shown an equivalent circuit of theparametric amplifier device of FIG- URES l-4 in which a pair of parallelinductive transmission lines 59 and 51 represent the wave guidestructure, and a third parallel inductive transmission line 52represents the center conductor. Reactance diodes 12, 13, 14', 15', 21',22' and 23', corresponding to the diodes in FIGURE 2, into which islumped distributed capacitance, are shown coupled between the outertransmission lines 50 and 51 and the center transmission line 52.Capacitances 53, 54 and 55 corresponding to the effective capacitance ofthe loading stubs in FIGURE 1, are shown coupled between the outertransmission lines 50 and 51. The pump wave is inductively coupled tothe input of transmission lines 50 and 51, and the signal Wave isinductively coupled to the input of the center transmission line 52.Inductive coupling is provided at the output of transmission lines 50and 51 and at the output of line 52 for the exiting pump and signalwaves, respectively. The idler wave is shown coupled to the signal wavecircuit.

Let us now examine the Brillouin diagrams of FIGURE 6 in which thefrequencies of the three traveling waves w are plotted versus theirphase constants B. The value of w/B for the curves shown will beappreciated to be the phase velocity V, of the various waves transmittedthrough their respective transmission media. Further, it can bemathematically proven that the velocity of the energy of propagation inthe longitudinal direction, or the group velocity V is equal to theslope of the w-B curves. Brillouin, or (0 versus [3, diagrams can bereadily constructed for any given transmission medium bywell knowntechniques, as disclosed, e.g., in D. A. Watkins Topics inElectromagnetic Theory.

The 40-13 curve for the signal wave is seen to be linear at the lowerfrequencies, exhibiting dispersion and becoming nonlinear at the upperfrequency region. By dispersion it is meant that the slope of the curveis not equal to a constant, and coincidentally dispersion causes theslope to pass through a zero value where the frequency is constant for achanging phase constant. The dispersion of the periodic reactive loadingof the wave. It is seen that the zero slope of the signal w-fl curveoccurs at a value of where a is the distance between the loadingreactance diodes, as indicated in the equivalent circuit of FIGURE 5.The phase velocity V, of the signal wave is negative. In accordance withthe present embodiment, the phase velocity V, of the idler wave, as afunction of the frequency, is equal in magnitude and opposite indirection to V so that the (0-5 curves for the two Waves are the mirrorimage of each other, and accordingly the zero slope of the idler waveoccurs at a value of ,8=+1r/a, It may be appreciated that individualtransmission paths may be employed for the signal and idler waves, inwhich instance the phase velocities of the signal and idler waves can beunequal.

The w-B curve for the pump wave is dispersive in the lower frequencyregion due to cut-off properties of the wave guide in which it ispropagated, becoming linear in an intermediate frequency range and againdispersive in the upper frequency region as a function of the periodicloading of the pump energy. It is seen that the zero slope of the curvein the upper frequency region occurs at a value of /3=+1r/ b, where b isthe distance between the periodic loading elements applied to the pumpwave, which is the distance between a loading stub and the adjacentreactance diode, as indicated in FIGURE 5. For values of b=a/2, themagnitude of 3 of the pump Wave is twice the magnitude of ,B of thesignal and idler waves at the zero slope points.

It may be analytically demonstrated that the value of [3 at the zeroslope points of the w-B curves is a function of the loading periodicityfrom the following considerations. As is well known, the equivalentcircuit of a transmission line may be considered as a succession ofidentical 11- type LC circuits each composed of a single inductance Lcoupled at either end by a pair of capacitances C to a reference plane.The resonant frequency w, of each LC circuit may be defined as It willbe appreciated that the resonant frequency corresponds to the frequencyat which the slope of the w-fi curve of the transmission line is zero,the energy having zero velocity in the longitudinal direction at thisfrequency. Since the phase constant p is defined as [3:21r/ A, thecoupled LC circuits at the resonant frequency have a value of fi=1r/S,where s is the spatial dimension between capacitances, since there is aphase shift between capacitances. By increasing the periodicity of thecapacitive loading, so that the spatial dimension s is decreased, thevalue of ,8 at the resonant frequency is seen to increase.

In addition an increase in the loading periodicity constitutes adecrease in the value of L and/ or C in Equation 1, thereby increasing oas well as B. For example, by loading with twice the number ofcapacitances all of the value C, thereby doubling the periodicity, thefollowing expression for the new resonant frequency w, is obtained:

wag/a3. (3)

A further increase in the periodicity provides a corresponding increasein the co If the value of C of the additional loading is reduced, wehave still a further increase in no In accordance with the aboveexplanation, the w,8 curve for the pump wave is expanded by additionalloading perturbation as shown in FIGURE 6, thereby providing an enhancedtuning range of the signal and a high idler frequency relative to thesignal frequency, as will now be demonstrated.

Assume an initial signal frequency of w coupled to the input terminalsof the amplifier. By tuning pump source Thus,

4 of FIGURE 1, the pump frequency is adjusted to w so as to provide anidler frequency ca on the dispersive portion of the idler w-B curve sothat w =w +w By pro-' viding the proper relationship between the phasevelocities of the three waves at the operation frequencies, the waveswill also be related by fip1 p 1'+l3u, and parametric amplificationoccurs. It is seen that the operating points with the origin form aparallelogram A. The recited in and ,8 constraints as well as thedesired operation on the dispersive portion of the idler w-fl curve forimproved tuning is described in detail in our above referred tocopending application. It is noted that although operation on the dispersive portion of the idler w-B curve is highly desirable, thisinvention is not dependent upon such operation and is of generaladvantage where an increased pump frequency is desired.

As w changes, e.g., to w w is changed by approximately the same amountto w and the idler frequency changes to which is approximately equal to01 At these points fl g=fi +fl As the signal changes to the pump istuned to M 3, [3 and the idler wave assumes a value of 0 5, so that thew and 5 constraints are again satisfied, parallelogram B being drawn.From an inspection of the w-fi curves of FIGURE 6, it is seen that, overa given tuning range, the group velocities of the signal wave aredifferent from the corresponding parametrically interacting groupvelocities of the idler wave, it being necessary that they be differentin magnitude or direction, or both, in order that selective tuning ofthe signal be provided.

It is seen that by expanding the w-B curve of the pump wave byadditional loading of the pump energy so that the dispersive portionoccurs at a higher value of w and B, that part of the pump w-,8 curvewhich is operated on is substantially linear. This provides access tohigher pump frequencies which allow greater flexibility in determiningthe value of the idler phase velocity and frequency, and the advantageof tuning to a wider band of signal frequencies as well as to highervalue signal frequencies. Thus, without the additional pump loading theupper frequency portion of the 19-5 pump curve would be as shown by thedashed line with the Zero slope occurring at l3=+7r/ a. It is seen thatoperation on the dashed pump curve for the same idler operation providesa maximum pump frequency at w ,8 and signal tuning from w to 6053, whichis a range considerably narrower than the band (.0 to r0 The increasedperturbation of the pump wave has the additional advantage of permittingthe idler frequency at the dispersive portion to be made greater, whichprovides a lower noise figure since the idler noise figure increaseswith the ratio of w /w It may be appreciated that by increasing theslope of the positive linear portion of the idler w-{3 curve so that theidler phase velocity approaches the pump phase velocity at the linearportions of their w-[i curves, the minimum signal frequency in thetuning band can be lowered.

To restate the advantages of the present invention, assume giventransmission paths for the signal, pump and idler waves characterized bygiven w-B curves for the three waves. If a maximum tuning range of thesignal is desired especially having relatively high value upperfrequencies, the phase velocity of the linear portion of the signal w-Bcurve, which is approximately its slope in this portion, is required tobe relatively high. Since the idler frequency must be higher than thesignal frequency for desirable noise figure, it may be found that therequired high pump frequencies necessary to tune the high signalfrequencies are not available due to the dispersive portion of the pumpw-fl curve. With additional perturbations of the pump energy whichexpands its w,B curve, as explained heretofore, the required higher pumpfrequencies appearing now on the linear part of the pump w-B curve canbe reached for tuning to the higher signal frequencies. Since the lowerportion of the w[3 curve is not effectively altered, lower signalfrequencies can also be tuned by modifying the idler 0 8 curve.

Referring now to FIGURE 7, there is illustrated in perspective viewanother embodiment of our invention, in which the transmission path forthe signal and idler Waves is structurally isolated from the pump wave.The amplifier device 60 includes a wave guide structure 61 composed ofwide dimension walls 62 and 63 and narrow dimension Walls 64 and 65, andhaving an input connector 66 and an output connector 67. A pump source4, which may be identical to that shown in FIGURE 1, is connected to theinput connector 66 for propagating the pump wave through the wave guide.The pump wave is terminated in a load 9 which is coupled to outputconnector 67. An enclosed compartment 68 is attached to the narrowdimension wall 64, which compartment encloses a center conductor 69running axially through the compartment, as shown in FIGURES 8, 9 and10. The center conductor 69 is provided with periodic undulations,similar to the conductor shown in FIGURE 3 and can support propagationof both the signal and idler waves. Compartment 68 has an inputconnector 70 and an output connector 71. A signal source 2, which may beidentical to the signal source of FIGURE 1, is connected to inputconnector 70. The amplified signal is coupled from output connector 71to signal load 7.

Twelve transverse conductors arranged in pairs, of which 72, '73, 74,75, 76, 77, 78 and 79 are shown in FIG- URES 8, 9 and 10, are enclosedin the wave guide structure 61, running transversely across said waveguide parallel to the wide dimension walls 62 and 63 and secured to thenarrow dimension walls 64 and 65. Twelve matched reactance diodesarranged in pairs of which 80, 81, 82, 83, S4, 85, 86 and 87 are shownin FIGURES 8, 9 and 10, are each coupled from center conductor 69 to acorresponding one of the transverse conductors. The diodes of each pairare poled in opposite directions. Each pair of diodes has coupledthereto tuning stubs 88 for matching the capacitive characteristics ofthe diodes. Twelve additional tuning stubs 89 are inserted through thewide dimension walls 62 and 63 into the hollow portion of the wave guide61 and adjacent to the transverse conductors. These stubs disturb thefields within the guide so as to couple the pump energy to thetransverse conductors. The pump, signal and idler waves react across thereactance diodes to provide parametric amplification, the pump energybeing coupled to the diodes by the transverse conductors.

In addition, there are provided ten loading stubs arranged in pairs ofwhich 90, 91, 92, 93, 94 and 95 are shown in FIGURES 8 and 10. Theloading stubs are inserted in the walls 62 and 63 at points intermediatethe stubs 89 and provide additional perturbations to the pump energyonly since they are offset from the transverse conductors andefiectively are not coupled to the signal and idler waves.

The operation of this embodiment of the present invention is similar tothat of FIGURES 1 to 4. The transmission paths for the pump, signal andidler waves provide w-B diagrams similar to those appearing in FIG- URE6, and tuning of the signal wave over an enhanced tuning range may beaccomplished as previously explained.

Although our invention has been disclosed in specific configurations,this has been done primarily for the purpose of clearly setting forththe invention. It should be recognized, therefore, that the basicprinciple underlying the invention may be embodied in a number of otherconfigurations without exceeding the teachings of the invention.Accordingly, the invention also has application to forward travelingparametric amplifiers, for example, of the type disclosed in ourpreviously referred to copending application. In addition, although waveguides and strip line conductors have been employed in the illustratedembodiments, the invention ha equal application to other forms oftransmission lines in which traveling 9 waves can occur as representedin the equivalent circuit of FIGURE 5.

Further, the loading reactance elements need not be periodically spacedas disclosed, which is primarily for the purpose of minimizingreflections of the propagated energy and to obtain uniform amplificationover the tuning range of the signal frequency, but operation of theparametric device in accordance with the invention may also beaccomplished with a non-uniform spacing of the reactance elements.Similarly, the additional loading stubs coupled to the pump energy neednot be periodically spaced but may be of a random nature, although auniform spacing may be desirable for good impedance matching. It shouldalso be recognized that additional loading of the pump energy may beaccomplished by either linear or nonlinear impedance means since theessential characteristic of this loading means is to control thedispersive property of the pump energy and is independent of anyparametric amplification effects.

In addition, further perturbations of the pump wave may be had byincreasing the number of loading stubs between successive reactancediodes, for example, making the dimension b of FIGURE equal to a/3, a/4or smaller.

The appended claims are intended to include all such modifications asfall within the true scope and spirit of the invention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. A tunable traveling wave parametric amplifier comprising a multipathtransmission line the paths of which support a signal wave of frequencym and phase constant 5 a pump wave of frequency u and phase constant[3,, and an idler wave of frequency m and phase constant 3;, where w =w+w and fi =fl +p said paths being constructed so as to provide signalgroup velocities that are different from corresponding parametricallyinteracting idler group velocities over the signal tuning range, loadingmeans including nonlinear reactance means coupled to said paths forsuccessively loading the pump wave at more frequent intervals than saidsignal and idler waves so as to extend the frequency range over whichthe pump wave can be propagated, said pump, signal and idler wavesreacting across said nonlinear reactance means to provide, in responseto adjustment of the pump frequency, parametric amplification of saidsignal wave over an enhanced range of signal frequencies.

2. A tunable traveling wave parametric amplifier comprising a multipathtransmission line the paths of which support a signal wave of frequencym and phase constant a a pump wave of frequency ta and phase constant3,, and an idler wave of frequency 01 and phase constant ,6 where w =w+w and fi =fl +fl said paths being constructed so as to provide signalgroup velocities that are different from corresponding parametricallyinteracting idler group velocities over the signal tuning range, aplurality of nonlinear reactance elements coupled to said paths forperiodically loading said transmission line so as to effect parametricamplification of the signal wave, said nonlinear reactance elementscausing dispersion in the w versus ,8 function of said paths, where w isthe frequency and B is the phase constant of the waves supportedthereby, a plurality of additional impedance element coupled to the pumppath for providing loading of the pump wave at a greater periodicitythan that of the signal and idler waves so that the near zero slopedispersive portion of the pump to versus 5 function occurs at increasedvalues of w and ,8, thereby extending the frequency range over which thepump wave can be propagated and providing tuning of the signal wave overan enhanced frequency band.

3. A tunable traveling wave parametric amplifier comprising a multipathtransmission line, the paths of which support a signal wave of frequency(.0 and phase constant [-3 a pump wave of frequency o and phase constant,8

and an idler wave of frequency w, and phase constant m, where w =w +wand B =/8 +fl said paths being constructed so as to provide signal groupvelocities that are different from corresponding parametricallyinteracting idler group velocities over the signal tuning range, aplurality of nonlinear reactance diode elements coupled to said paths atpredetermined intervals for successively loading said transmission lineso as to effect parametric amplification of the signal wave, said diodeelements cauing dispersion in the w versus 18 function of said paths,where w is the frequency and B is the phase constant of the wavessupported thereby, additional impedance ele ments coupled to the pumppath for providing loading of the pump wave at intervals more frequentthan said predetermined intervals so that the near Zero slope dispersiveportion of the pump w versus ,3 function occurs at increased values of wand ,8, thereby extending the fre quency range over which the pump wavecan be propagated and providing tuning of the signal Wave over anenhanced frequency band.

4. A tunable traveling wave parametric amplifier for amplifying a signalwave of frequency m and phase constant ,8, by a mixing operation whichconverts power from a pump wave of frequency u and phase constant 5,,through an idler wave of frequency w, and phase constant 5,, where w =w+w and ,B ,=,B +,B comprising a multipath transmission line the paths ofwhich are constructed so as to provide signal group velocities that aredifferent from corresponding parametrically interacting idler groupvelocities over the signal tuning range, said transmission lineincluding a wave guide structure the walls of which enclose at least oneconductor running longitudinally through said wave guide, said pump wavebeing propagated through said wave guide and said signal wave beingpropagated along said conductor, said idler wave being supported by oneof the paths of said transmission line, a plurality of nonlinearreactance elements coupled between said conductor and the walls of saidwave guide for successively loading the paths of said transmission lineat predetermined intervals, said pump, signal and idler waves reactingacross said nonlinear reactance means to provide parametricamplification of said signal wave, a plurality of additional impedanceelements coupled between the walls of said wave guide and essentiallyuncoupled from said conductor for successively loading said pump wave atintervals more frequent than said predetermined intervals, whereby saidwave guide propagates a wide range of pump frequencies so as to permittuning of the signal wave over an enhanced frequency band.

5. A tunable traveling wave parametric amplifier for amplifying a signalwave of frequency m and phase constant ,8 by a mixing operation whichconverts power from a pump wave of frequency u and phase constant ,Bthrough an idler wave of frequency w, and phase constant ,8 where w =w+w and ,fi =fi +li comprising a multipath transmission line the paths ofwhich are constructed so as to provide signal group velocities that aredifferent from corresponding parametrically interacting idler groupvelocities over the signal tuning range, said transmission lineincluding a wave guide structure the walls of which enclose at least oneconductor of undulatory construction running longitudinally through saidwave guide, said pump wave being propagated through said wave guide andsaid signal wave being propagated along said conductor, said idler wavebeing supported by one of the paths of said transmission line, aplurality of nonlinear reactance diode elements spaced along the lengthof the transmission line and coupled between said conductor and thewalls of said wave guide for successively loading the paths of saidtransmission line at predetermined intervals so that said pump, signaland idler waves react across said diodes to provide parametricamplification of said signal wave, a plurality of loading stubs coupledbetween the walls of said wave guide, said loading stubs beingpositioned at points intermediate said diodes and transversely displacedtherefrom so as to be essentially uncoupled from said conductor, saidloading stubs providing a successive loading of the pump wave atintervals more frequent than said predetermined intervals, whereby saidwave guide propagates a Wide range of pump frequencies so as to permittuning of the signal wave over an enhanced frequency band.

6. A tunable traveling wave parametric amplifier for amplifying a signalof frequency m and phase constant [i by a mixing operation whichconverts power from a pump wave of frequency w and phase constant ,Bthrough an idler wave of frequency w and phase constant {3 where w =w +wand fl =fi +l3 comprising a multipath transmission line the paths ofwhich are constructed so as to provide signal groups velocities that aredifferent from corresponding parametrically interacting idler groupvelocities over the signal tuning range, said transmission lineincluding a wave guide structure having a pair of wide dimensioned wallsand a pair of narrow dimensioned walls, an adjacent enclosed conductorin axial alignment with said wave guide structure, said pump wave beingpropagated through said wave guide and said signal wave being propagatedalong said conductor, a plurality of transverse conductors forsupporting said idlerwave coupled along the length of said wave guidebetween said narrow dimensioned walls, a plurality of nonlinearreactance elements coupled between said enclosed conductor and saidtransverse conductors for successively loading the paths of saidtransmission line at predetermined intervals, said pump, signal andidler waves reacting across said nonlinear reactance elements to provideparametric amplification of said signal wave, a plurality of additionalimpedance ele ments coupled between said wide dimensioned walls andessentially uncoupled from said transverse conductors for providingsuccessive loading of said pump wave at intervals more frequent thansaid predetermined intervals, whereby said wave guide propagates a widerange of pump frequencies so as to permit tuning of the signal wave overan enhanced frequency band.

References Cited by the Examiner UNITED STATES PATENTS ROY LAKE, PrimaryExaminer.

FREDERICK M. STRADER, D. R. HOSTETTER,

Assistant Examiners.

1. A TUNABLE TRAVELING WAVE PARAMETRIC AMPLIFIER COMPRISING A MULTIPATHTRANSMISSION LINE THE PATHS OF WHICH SUPPORT A SIGNAL WAVE OF FREQUENCYWS AND PHASE CONSTANT BS, A PUMP WAVE OF FREQUENCY WP AND PHASE CONSTANTBP AND AN IDLER WAVE OF FREQUENCY WI AND PHASE CONSTANT BI, WHEREWP=WS+WI AND BP=BS+BI, SAID PATHS BEING CONSTRUCTED SO AS TO PROVIDESIGNAL GROUP VELOCITIES THAT ARE DIFFERENT FROM CORRESPONDINGPARAMETRICALLY INTERACTING IDLER GROUP VELOCITIES OVER THE SIGNAL TUNINGRANGE, LOADING MEANS INCLUDING NONLINEAR REACTANCE MEANS COUPLED TO SAIDPATHS FOR SUCCESSIVELY LOADING THE PUMP WAVE AT MORE FREQUENT INTERVALSTHAN SAID SIGNAL AND IDLER WAVES SO AS TO EXTEND THE FREQUENCY RANGEOVER WHICH THE PUMP WAVE CAN BE PROPAGATED, SAID PUMP, SIGNAL AND IDLERWAVES REACTING ACROSS SAID NONLINEAR REACTANCE MEANS TO PROVIDE, INRESPONSE TO ADJUSTMENT OF THE PUMP FREQUENCY, PARAMETRIC AMPLIFICATIONOF SAID SIGNAL WAVE OVER AN ENHANCED RANGE OF SIGNAL FREQUENCIES.